1. Field of the Invention
This invention related to internal combustion engines and their operation, and in particular to a development of the invention disclosed in our co-pending U.K. Patent application no. 9016813.9.
2. Discussion of Prior Art
In said co-pending application, timing of the opening and closing of an inlet valve of a combustion chamber is controlled so that its opening creates an in-flow to the chamber to create turbulence, which thereafter assists combustion. Preferably between ignitions in the engine's cycle there are two openings of a single inlet valve, two separate inlet valves opening once each or separate openings of an exhaust valve and an inlet valve.
However, with engines having two inlet valves per cylinder, and a separate camshaft for each such valve, there is a difficult compromise between the rate of valve opening defined by the cam profile, the intensity of turbulence and pumping work.
In an ideal case, the first and second inlet valve openings would, at light load, be of short duration. The first valve would open near to TDC and its closing would not be too late in the induction stroke otherwise the pressure differential developed across the second inlet valve by the time of its opening would be inadequate to produce the desired `blowdown` turbulence. The second valve closing time is fixed by the requirement to trap the desired mass of mixture in the cylinder, and the opening of the second valve should be as late as possible so that the blowdown turbulence has only a short time to decay. At 6000 RPM, the stress on the nose of the cam and cam follower controlling the inlet valves is high with conventional opening periods. To operate with periods of approximately half these values for the double induction process would force either a much lower RPM limit or a much reduced valve lift. Both of these actions would reduce maximum power available to meet full load demand.
An object of the invention is to overcome this difficulty.
According to the invention there is provided a method of operating an internal combustion engine having an inlet manifold, at least one combustion chamber with at least two inlet valves and at least one outlet valve, a piston reciprocable in the or each chamber to define a variable volume space therein, and means for controlling the timing of the opening and closing of each of two of the inlet valves of the or each chamber independently, the method comprising opening one of the independently controlled inlet valves of the or each chamber during the exhaust stroke of the engine, producing first and second pressures in the inlet manifold and the at least one chamber respectively, said first pressure being greater than said second pressure, whereby opening of the other of the independently controlled inlet valves of the or each chamber, at a time when said one of the independently controlled inlet valves is closed and while this predetermined pressure differential exists, creates an in-flow into the or each chamber generating turbulence, at least some of which is present when combustion occurs in the or each chamber.
According to another aspect of the invention there is provided an internal combustion engine comprising an inlet manifold, at least one combustion chamber with at least two inlet valves and at least one outlet valve, a piston reciprocable in the or each chamber to define a variable volume space therein, and means for controlling the timing of the opening and closing of each of two of the inlet valves of the or each chamber independently so that opening of one of the independently controlled inlet valves of the or each chamber occurs during the exhaust stroke of the engine, opening of the other of the independently controlled inlet valves of the or each chamber, at a time when said one of the independently controlled inlet valves is closed, and when pressure in the or each chamber is lower than pressure in said inlet manifold, producing a predetermined pressure differential across said other of the independently controlled inlet valves, creating an in-flow to the or each chamber generating turbulence, at least some of which is present when combustion occurs in the or each chamber.
The expressions `induction stroke`, `compression stroke` and `exhaust stroke` as used herein are intended to have their usual meanings in relation to a piston of a four stroke engine, notwithstanding the opening and closing of inlet and exhaust valves at timings different from the normal relative to said strokes.